Pork is cooked when its internal temperature reaches 160F/71C. At this temperature, the pork may still be pink and moist inside. That's OK! If you don't have a meat thermometer, the only way to be sure that the meat is safely cooked is to wait until it is no longer pink inside - at which point it may be dry and overcooked. The moral of this story: get a meat thermometer!

What are "medallions", anyway? They are just slices of pork tenderloin! Slice the pork about 3/4 of an inch thick.